Damage Measurement of Structural Material by Electron Backscatter Diffraction (Quantification of Measurement Quality toward Standardization of Measurement Procedure)

Abstract

Several attempts have been made to assess the damage induced in materials by crystal orientation distributions identified using electron backscatter diffraction (EBSD). However, the error in crystal orientation measurements makes quantitative evaluation of the local misorientation difficult. Furthermore, the local misorientation depends on distance between the measurement points (step size). For a quantitative assessment of the local misorientation, the error in the crystal orientation measurements must be reduced or the degree of error must be shown quantitatively. In this study, first, the influence of the quality of measurements (accuracy of measurements) and step size on the local misorientation was investigated using stainless steel specimens damaged by tensile deformation or fatigue. By performing the crystal orientation measurements with different conditions, it was shown that the quality of measurement could be represented by the error index, which was previously proposed by the author. Secondly, a filtering process was applied in order to improve the accuracy of crystal orientation measurements and its effect was investigated using the error index. It was revealed that the local misorientations obtained under different measurement conditions could be compared quantitatively only when the error index and the step size were almost or exactly the same. It was also shown that the filtering process could successfully reduce the measurement error and step size dependency of the local misorientations. By applying the filtering process, almost identical local misorientations distributions were obtained under different measurement conditions. Finally, for standardization of the measurement procedure of the local misorientation, present knowledge and points to note about measurements were summarized.